1. Field of the Invention
The present invention relates to a semiconductor device and an audio processor chip, and particularly to a semiconductor device and an audio processor chip used for a mobile phone.
2. Description of Related Art
With advances in multi-functionalization and higher performance of mobile phones, mobile phones equipped with data communication function and audio playback function as audio equipment in addition to the original call function with voice have been developed.
As for the audio playback process in a mobile phone, for example audio data downloaded via the network and audio data recorded on recording media such as a removable memory is decoded by a processor of the mobile phone. The decoded data is converted into an analog signal by a D/A converter and is played back by a loudspeaker through a mixing process.
Such mobile phone has been spreading to take the place of dedicated audio playback device and higher performance is required for audio playback.
On the other hand, as described in Japanese Unexamined Patent Application Publication No. 2001-345731, miniaturization and reduction of power consumption in mobile phones are also required due to the characteristics of the mobile phone to be carried along.
Since there is control of power consumption during audio playback for a long time and audio codec that cannot be processed by a processor of a mobile phone, an audio processor only for audio playback is used. In order to distinguish from this audio processor, the processor of the mobile phone stated above is hereinafter referred to as a main processor.
By providing the audio processor, it is possible to playback the audio codec that cannot be processed by the main processor and also to control the power consumption as the main processor can be in a standby state during audio playback for a long time and thereby achieving higher performance.
As for audio playback, a mobile phone of a related art and a mobile phone having an audio processor are compared here.
FIG. 3 shows the pattern diagram of the processing portion concerning audio in the mobile phone of a related art. Usually, in a mobile phone, processes such as application and communication are performed by a chip provided in the platform. As shown in FIG. 3, a DBB 10, an AFE 20 and a clock generation circuit 30 are provided in a platform 1 indicated by DBB PF in FIG. 3. Note that DBB, DBB PF and AFE respectively mean Digital Baseband, Digital Baseband Platform and Analog Front End.
The DBB 10 is a main processing chip having a main processor and a communication processing unit and as for voice processing, decodes audio data and outputs it to the AFE 20.
The AFE 20 is a voice processing chip and includes a DAC (D/A converter) 22 for converting digital data from the DBB 10 into an analog signal and an analog mixer 24 for performing a mixing process to the analog signal obtained from the DAC 22 and outputting to a playback device such as a loudspeaker.
The clock generation circuit 30 generates a clock signal for the DAC 22 of the AFE 20 and supplies it to the DAC 22. In addition, the DAC 22 operates as a clock master circuit of the DBB 10 and the clock signal is to be a master clock (LRCLK and BCLK in the drawings) used when the DBB 10 decodes audio data.
Note that the DBB 10, the AFE 20 and the clock generation circuit 30 are connected to a system bus 40 and the DBB 10 also performs motion control of the AFE 20 and the clock generation circuit 30 via the system bus 40.
When adding an audio processor to the configuration shown in FIG. 3, the pattern shown in FIG. 4 can be considered. As shown in FIG. 4, in addition to each component provided in the platform 1, an audio processor 50 having a DSP (Digital Signal Processor) 52 for decoding audio data, a DAC 54 for converting the data decoded by the DSP 52 into an analog signal and a clock generation circuit 56 for generating a clock signal for the DAC 54 is provided. Note that the analog signal obtained by the DAC 54 is output to the analog mixer 24 of the AFE 20, a mixing process is performed by the analog mixer 24 and then output to a loudspeaker etc.
Moreover, the audio processor 50 is also connected to the system bus 40 and is controlled by the DBB 10 via the system bus 40.
According to the configuration shown in FIG. 4, audio processing can be performed by different processing units depending on the case of usual telephone call and short-time audio playback (hereinafter referred to as a first case) and the case of long-time audio playback and audio codec that cannot be processed by the DBB 10 (hereinafter referred to as a second case).
For example, in the first case, data decoded by the DBB 10 is output to the DAC 22 of the AFE 20. After that, the DAC 22 performs a D/A conversion, obtains an analog signal, outputs it to the analog mixer 24 and a mixing process is performed by the analog mixer 24.
On the other hand, in the second case, the DBB 10 transmits a control signal to the audio processor 50 via the system bus, for example, to operate. The audio processor 50 starts operation in response to the control signal. Specifically, the DSP 52 decodes audio data and outputs the decoded data to the DAC 54. The DAC 54 performs a D/A conversion to the digital data from the DSP 52, obtains an analog signal and outputs this analog signal to the analog mixer 24 of the AFE 20. The analog mixer 24 performs a mixing process to the analog signal and outputs it to a loudspeaker. The clock generation circuit 56 generates a clock signal for the DAC 54 and supplies it to the DAC 54. Note that also in the audio processor 50, the DAC 54 operates as a clock master circuit of the DSP 52, generates a clock signal to be used by the DSP 52 at the time of decoding from the clock signal used by the DAC 54 and supplies it to the DSP 52.
As the power consumption while the audio processor 50 is operating is less than power consumption while the DBB 10 is operating, in the second case, the DBB 10 controls to let the audio processor 50 starts operation and can be in the standby state later on with the configuration shown in FIG. 4. Thus it is possible to save the power consumption. Furthermore, audio playback with higher performance can be offered by the audio processor 50.
As mentioned above, along with the reduction of power consumption in mobile phones, the miniaturization of mobile phones is an important subject in developing mobile phones and can be said to be one of the parameters that influence the competitiveness of mobiles phones. Therefore, it is required to spare no effort to reduce circuit size of mobiles phones and eventually each functional component used in mobile phones. The inventor of the present invention proposes a technique which can reduce a circuit size also for mobile phones provided with the audio processor only for audio playback in order to realize advanced audio playback function.